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{{Short description|In astronomy, a dynamical group of trans-Neptunian objects}}
{{about-distinguish-text|the dynamical group|[[plutoid]]s or [[pluton]]s}}

In [[astronomy]], the '''plutinos''' are a [[List of minor-planet groups|dynamical group]] of [[trans-Neptunian object]]s that orbit in 2:3 [[orbital resonance|mean-motion resonance]] with [[Neptune]]. This means that for every two orbits a plutino makes, Neptune orbits three times. The dwarf planet [[Pluto]] is the largest member as well as the namesake of this group. The next largest members are {{dp|Orcus}}, [[208996 Achlys|Achlys]], and {{dp|Ixion}}. Plutinos [[Astronomical naming conventions#Minor planets|are named after]] mythological creatures associated with the underworld.

Plutinos form the inner part of the [[Kuiper belt]] and represent about a quarter of the known [[Kuiper belt object]]s. They are also the most populous known class of [[resonant trans-Neptunian object]]s ''(also see adjunct box with hierarchical listing)''. The first plutino after Pluto itself, [[(385185) 1993 RO]], was discovered on September 16, 1993.

== Orbits ==
[[Image:ThePlutinos Size Albedo Color2.svg|thumb|right|210px|Some of the largest known plutinos compared in size, [[albedo]] and [[color index|colour]]]]

=== Origin ===
It is thought that the objects that are currently in mean [[orbital resonance]]s with Neptune initially followed a variety of independent heliocentric paths. As Neptune migrated outward early in the Solar System's history (see [[Kuiper belt#Origin|origins of the Kuiper belt]]), the bodies it approached would have been scattered; during this process, some of them would have been captured into resonances.<ref name="Malhotra1995">{{cite journal |last1=Malhotra |title=The Origin of Pluto's Orbit: Implications for the Solar System Beyond Neptune |journal=Astronomical Journal |volume=110 |year=1995 |page=420 |arxiv = astro-ph/9504036 |bibcode = 1995AJ....110..420M |doi = 10.1086/117532 |first1= Renu|s2cid= 10622344}}</ref> The 3:2 resonance is a low-order resonance and is thus the strongest and most stable among all resonances.<ref>{{cite journal|last1=Almeida|first1=A.J.C|last2=Peixinho|first2=N.|last3=Correia|first3=A.C.M. |url=https://www.researchgate.net/publication/45876510|title=Neptune Trojans & Plutinos: Colors, sizes, dynamics, & their possible collisions|date=December 2009|journal=Astronomy & Astrophysics|doi=10.1051/0004-6361/200911943|volume=508|issue=2|pages=1021–1030|access-date=2019-07-20|arxiv=0910.0865|s2cid=53772214}}</ref> This is the primary reason it has a larger population than the other Neptunian resonances encountered in the Kuiper Belt. The cloud of low-inclination bodies beyond 40 [[Astronomical unit|AU]] is the [[Classical Kuiper belt object|cubewano]] family, while bodies with higher [[Orbital eccentricity|eccentricities]] (0.05 to 0.34) and [[Semi-major and semi-minor axes|semi-major axes]] close to the 3:2 Neptune resonance are primarily plutinos.<ref>{{cite book|url=https://books.google.com/books?id=QpcKesJwp28C&pg=PA411|first=John S.|publisher=Academic Press|department=Centaurs & Trans-Neptunian Objects|last=Lewis|isbn=012446744X |title=Physics & Chemistry of the Solar System|date=2004|pages=409–412|access-date=2019-07-21}}</ref>

=== Orbital characteristics ===
[[File:Plutino distributions and sizes.png|thumb|The distribution of Plutinos, and relative sizes, drawn 1 million times larger.]]
While the majority of plutinos have relatively low [[orbital inclination]]s, a significant fraction of these objects follow orbits similar to that of Pluto, with inclinations in the 10–25° range and eccentricities around 0.2–0.25; such orbits result in many of these objects having [[perihelion|perihelia]] close to or even inside Neptune's orbit, while simultaneously having [[aphelion|aphelia]] that bring them close to the main [[Kuiper belt]]'s outer edge (where objects in a 1:2 resonance with Neptune, the twotinos, are found).

The orbital periods of plutinos cluster around 247.3 years (1.5 × Neptune's orbital period), varying by at most a few years from this value.

Unusual plutinos include:
* [[List of unnumbered trans-Neptunian objects: 2005#2005 TV189|{{mp|2005 TV|189}}]], which follows the most highly inclined orbit (34.5°)
*{{mpl|(15875) 1996 TP|66}}, which has the most elliptical orbit (its eccentricity is 0.33), with the perihelion halfway between Uranus and Neptune
*{{mpl|(470308) 2007 JH|43}} following a quasi-circular orbit
* [[List of unnumbered trans-Neptunian objects: 2002#2002 VX130|{{mp|2002 VX|130}}]] lying almost perfectly on the [[ecliptic]] (inclination less than 1.5°)
*[[15810 Arawn]], a [[quasi-satellite]] of Pluto<ref name=analemma>{{cite journal |title=The analemma criterion: accidental quasi-satellites are indeed true quasi-satellites |first1=Carlos |last1=de la Fuente Marcos |last2=de la Fuente Marcos |first2=Raúl |journal=[[Monthly Notices of the Royal Astronomical Society]] |date=2016 |volume=462 |issue=3 |pages=3344–3349 |arxiv=1607.06686 |doi=10.1093/mnras/stw1833 |doi-access=free |bibcode=2016MNRAS.462.3344D}}</ref>

See also the comparison with the [[cubewano#Distribution|distribution of the cubewanos]].

=== Long-term stability ===
Pluto's influence on the other plutinos has historically been neglected due to its relatively small mass. However, the resonance width (the range of semi-axes compatible with the resonance) is very narrow and only a few times larger than Pluto's [[Hill sphere]] (gravitational influence). Consequently, depending on the original eccentricity, some plutinos will eventually be driven out of the resonance by [[Perturbation (astronomy)|interactions]] with Pluto.<ref name=wan2001>{{cite journal
  | author=Wan, X.-S
  |author2=Huang, T.-Y.
   | title=The orbit evolution of 32 plutinos over 100 million year
  | journal=Astronomy and Astrophysics
  | volume=368
  | issue=2 | pages=700–705 | year=2001
  | bibcode=2001A&A...368..700W| doi = 10.1051/0004-6361:20010056
| doi-access=free}}</ref>  Numerical simulations suggest that the orbits of plutinos with an eccentricity 10%–30% smaller or larger than that of Pluto are not stable over billion-year timescales.<ref name="Yu1999">{{cite journal |first1=Qingjuan |last1=Yu |first2=Scott |last2=Tremaine |title=The Dynamics of Plutinos |journal=Astronomical Journal |volume=118 |year=1999 |issue= 4|pages=1873–1881 |arxiv = astro-ph/9904424 |bibcode = 1999AJ....118.1873Y |doi = 10.1086/301045 |s2cid=14482507 }}</ref>

== Orbital diagrams ==
<gallery widths=250px heights=250px>
File:OrcusandPlutoRotatingFrame.gif|The motions of [[90482 Orcus|Orcus]] and [[Pluto]] in a [[rotating frame]] with a period equal to [[Neptune]]'s [[orbital period]] (holding Neptune stationary). Pluto is grey, Orcus is red, and Neptune is the white (stationary) dot at 5 o'clock. Uranus is blue, Saturn yellow, and Jupiter red.
File:TheKuiperBelt 60AU LargePlutinos.svg|Orbits and sizes of the larger plutinos (and the reference non-plutino {{mpl-|119951|2002 KX|14}}). Orbital [[eccentricity (orbit)|eccentricity]]  is represented by segments extending horizontally from [[perihelion]] to [[aphelion]]; [[inclination]] is shown on the vertical axis.
File:TheKuiperBelt 60AU Plutinos distribution.svg|The distribution of plutinos (and the reference non-plutino {{mp|2002 KX|14}}). Small inserts show [[histogram]]s for the distributions of orbital inclination and eccentricity.
</gallery>

== Brightest objects ==
The plutinos brighter than H<sub>V</sub>=6 include:
{| class="wikitable sortable" style="width:100%; text-align:center; font-size: 0.9em;"
! Object !! [[Semi-major axis|a]]<br />(AU) !! [[Perihelion|q]]<br />(AU) !! [[Inclination|i]]<br />(°) !! [[Absolute magnitude#Solar System bodies (H)|H]] !! Diameter<br />(km) !! Mass<br />(10<sup>20</sup> kg) !! [[Albedo#Astronomical albedo|Albedo]] !! [[Distant object color indices|V−R]] !! Discovery<br />year !! Discoverer || Refs
|-
| [[134340 Pluto]] || 39.3 || 29.7 || 17.1 || data-sort-value="-0.7"|−0.7 || 2322 || 130 || 0.49–0.66 || || 1930 || [[Clyde Tombaugh]] || {{JPL|134340}}
|-
| [[90482 Orcus]] || 39.2 || 30.3 || 20.6 || data-sort-value="2.3"|{{val|2.31|0.03}} || data-sort-value="917"|{{val|917|25}} || {{val|6.32|0.05}} || {{val|0.28|0.06}} || 0.37 || 2004 || M. Brown,<br />C. Trujillo,<br />D. Rabinowitz || {{JPL|90482}}
|-
| [[208996 Achlys]] || 39.4 || 32.3 || 13.6 || data-sort-value="3.7"|{{val|3.74|0.08}} || data-sort-value="717"|{{val|727.0|+61.9|-66.5}} || ≈&thinsp;3 || {{val|0.107|+0.023|-0.016}} || {{val|0.38|0.04}} || 2003 || M. Brown,<br />C. Trujillo || {{JPL|208996}}
|-
| [[28978 Ixion]] || 39.7 || 30.1 || 19.6 || data-sort-value="3.8"|{{val|3.828|0.039}} || data-sort-value="617"|{{val|617|19|20}} || ≈&thinsp;3 || {{val|0.141|0.011}} || 0.61 || 2001 || [[Deep Ecliptic Survey]] || {{JPL|28978}}
|-
| {{mpl|(678191) 2017 OF|69}} || 39.5 || 31.3 || 13.6 || data-sort-value="4.09"|{{val|4.091|0.12}} || data-sort-value="530"|≈&thinsp;380–680 || ? || ? || ? || 2017 || [[David J. Tholen|D. J. Tholen]],<br />[[Scott S. Sheppard|S. S. Sheppard]],<br />[[Chad Trujillo|C. Trujillo]] || {{JPL|2017+OF69}}
|-
| {{mpl|(84922) 2003 VS|2}} || 39.3 || 36.4 || 14.8 || data-sort-value="4.1"|{{val|4.1|0.38}} || data-sort-value="523"|{{val|523.0|+35.1|-34.4}} || ≈&thinsp;1.5 || {{val|0.147|+.063|-.043}} || {{val|0.59|0.02}} || 2003 || [[Near Earth Asteroid Tracking|NEAT]] || {{JPL|84922}}
|-
| {{mpl|(455502) 2003 UZ|413}} || 39.2 || 30.4 || 12.0 || data-sort-value="4.4"|{{val|4.38|0.05}} || data-sort-value="600"|≈&thinsp;600 || ≈&thinsp;2 || ? || {{val|0.46|0.06}} || 2001 || M. Brown,<br />C. Trujillo,<br />D. Rabinowitz || {{JPL|455502}}
|-
| {{mpl|(556068) 2014 JR|80}} || 39.5 || 36.0 || 15.4 || data-sort-value="4.9"|{{val|4.9}} || data-sort-value="405"|≈&thinsp;240–670 || ? || ? || ? || 2014 || [[Pan-STARRS]] || {{JPL|2014+JR80}}
|-
| {{mpl|(578993) 2014 JP|80}} || 39.5 || 36.7 || 19.4 || data-sort-value="4.9"|{{val|4.9}} || data-sort-value="455"|≈&thinsp;240–670 || ? || ? || ? || 2014 || [[Pan-STARRS]] || {{JPL|2014+JP80}}
|-
| [[38628 Huya]] || 39.4 || 28.5 || 15.5 || data-sort-value="5.0"|{{val|5.04|0.03}} || data-sort-value="406"|{{val|406|16}} || ≈&thinsp;0.5 || {{val|0.083|0.004}} || {{val|0.57|0.09}} || 2000 || Ignacio Ferrin || {{JPL|38628}}
|-
| {{mpl|(469987) 2006 HJ|123}} || 39.3 || 27.4 || 12.0 || data-sort-value="5.3"|{{val|5.32|0.66}} || data-sort-value="283"|{{val|283.1|+142.3|-110.8}} || ≈&thinsp;0.012 || {{val|0.136|+0.308|-0.089}} || || 2006 || [[Marc W. Buie]] || {{JPL|469987}}
|-
| {{mpl|(612533) 2002 XV|93}} || 39.3 || 34.5 || 13.3 || data-sort-value="5.4"|{{val|5.42|0.46}} || data-sort-value="549"|{{val|549.2|+21.7|-23.0}} || ≈&thinsp;1.7 || {{val|0.040|+0.020|-0.015}} || {{val|0.37|0.02}} || 2001 || M.W.Buie  || {{JPL|2002+XV93}}
|-
| {{mpl|(469372) 2001 QF|298}} || 39.3 || 34.9 || 22.4 || data-sort-value="5.4"|{{val|5.43|0.07}} || data-sort-value="408"|{{val|408.2|+40.2|-44.9}} || ≈&thinsp;0.7 || {{val|0.071|+0.020|-0.014}} || {{val|0.39|0.06}} || 2001 || Marc W. Buie || {{JPL|469372}}
|-
| [[47171 Lempo]] || 39.3 || 30.6 || 8.4 || data-sort-value="5.4"|{{val|5.41|0.10}} || data-sort-value="393"|{{val|393.1|+25.2|-26.8}} <br />(triple) || {{val|0.1275|0.0006}} || {{val|0.079|+0.013|-0.011}} || {{val|0.70|0.03}} || 1999 || E. P. Rubenstein,<br />L.-G. Strolger || {{JPL|47171}}
|-
| {{mpl|(307463) 2002 VU|130}} || 39.3 || 31.2 || 14.0 || data-sort-value="5.5"|{{val|5.47|0.83}} || data-sort-value="253"|{{val|252.9|+33.6|-31.3}} || ≈&thinsp;0.16 || {{val|0.179|+0.202|-0.103}} || || 2002 || [[Marc W. Buie]] || {{JPL|307463}}
|-
| {{mpl|(84719) 2002 VR|128}} || 39.3 || 28.9 || 14.0 || data-sort-value="5.6"|{{val|5.58|0.37}} || data-sort-value="448"|{{val|448.5|+42.1|-43.2}} || ≈&thinsp;1 || {{val|0.052|+0.027|-0.018}} || {{val|0.60|0.02}} || 2002 || [[Near-Earth Asteroid Tracking|NEAT]] || {{JPL|84719}}
|-
| {{mpl|(55638) 2002 VE|95}} || 39.4 || 30.4 || 16.3 || data-sort-value="5.7"|{{val|5.70|0.06}} || data-sort-value="250"|{{val|249.8|+13.5|-13.1}} || ≈&thinsp;0.15 || {{val|0.149|+0.019|-0.016}} || {{val|0.72|0.05}}|| 2002 || [[Near Earth Asteroid Tracking|NEAT]] || {{JPL|55638}}
|}

(link to all of the orbits of these objects listed above are [https://www.spacereference.org/solar-system#ob=90482-orcus-2004-dw,455502-2003-uz413,469987-2006-hj123,55638-2002-ve95,84719-2002-vr128,84922-2003-vs2,208996-2003-az84,307463-2002-vu130,469372-2001-qf298,612533-2002-xv93,578993-2014-jp80,556068-2014-jr80,2017-of69,28978-ixion-2001-kx76,38628-huya-2000-eb173,47171-lempo-1999-tc36,134340-pluto-1930-bm here])

== See also ==
{{Portal|Astronomy}}

* [[Resonant trans-Neptunian object|Resonant Trans-Neptunian Object]]
* [[Twotino]]

== References ==
{{reflist}}
{{refbegin}}
* D.Jewitt, A.Delsanti ''The Solar System Beyond The Planets'' in ''Solar System Update : Topical and Timely Reviews in Solar System Sciences '', Springer-Praxis Ed., {{ISBN|3-540-26056-0}}  (2006). [https://web.archive.org/web/20060525051103/http://www.ifa.hawaii.edu/faculty/jewitt/papers/2006/DJ06.pdf Preprint of the article (pdf)]
* Bernstein G.M., Trilling D.E., Allen R.L., Brown K.E, Holman M., Malhotra R. ''The size Distribution of transneptunian bodies.'' The Astronomical Journal, '''128''', 1364–1390. [https://arxiv.org/abs/astro-ph/0308467 preprint on arXiv]
* Minor Planet Center Orbit database (MPCORB) as of 2008-10-05.
* Minor Planet Circular 2008-S05 (October 2008) [http://www.minorplanetcenter.org/mpec/K08/K08S05.html Distant Minor planets]  was used for orbit classification.
{{refend}}

== External links ==
* [http://www2.ess.ucla.edu/~jewitt/kb/plutino.html David Jewitt on Plutinos]
* [http://www.minorplanetcenter.org/iau/lists/TNOs.html Minor Planet Center, List of TNOs]
* [http://www.minorplanetcenter.org/mpec/K06/K06D28.html MPC List of Distant Minor Planets]

{{Solar System}}
{{Trans-Neptunian objects}}

[[Category:Plutinos| ]]
[[Category:Solar System]]